1. Field of invention
The invention relates to the field of liquid pumps in medical treatment devices.
2. Description of the Prior Art
Medical treatment devices are in particular blood treatment devices. Blood treatment devices comprise dialysis machines which can be subdivided into hemodialysis machines and machines for performing automated peritoneal dialyses.
Dialysis is a method of purifying the blood of patients with acute or chronic renal insufficiency. Fundamentally, a distinction is made here between methods having an extracorporeal blood circulation such as hemodialysis, hemofiltration or hemodiafiltration (summarized below under the term “hemodialysis”) and peritoneal dialysis, which does not have an extracorporeal blood circulation.
In hemodialysis the blood in an extracorporeal circulation is passed through the blood chamber of a dialyzer, which is separated from a dialysis fluid chamber by a semipermeable membrane. The dialysis fluid chamber has a dialysis fluid containing the blood electrolytes in a certain concentration flowing through it. The substance concentration of the dialysis fluid corresponds to the concentration of the blood of a healthy person. During the treatment, the patient's blood and the dialysis fluid are passed by both sides of the membrane, usually in countercurrent at a predetermined flow rate. Substances that must be eliminated in urine diffuse through the membrane from the blood chamber into the chamber for the dialysis fluid, while at the same time electrolytes present in the blood and in the dialysis fluid are diffusing from the chamber of the higher concentration to the chamber of the lower concentration. If a pressure gradient is built up from the blood side to the dialysate side on the dialysis membrane, for example, due to a pump which withdraws dialysate from the dialysate circulation downstream from the dialysis filter on the dialysate side, water enters the dialysate circulation from the patient's blood through the dialysis membrane. This ultrafiltration process leads to the desired withdrawal of water from the patient's blood.
In hemofiltration, ultrafiltrate is withdrawn from the patient's blood by applying a transmembrane pressure in the dialyzer without passing dialysis fluid by the membrane of the dialyzer on the side opposite the patient's blood. In addition, a sterile and pyrogen-free substitute solution may be added to the patient's blood. We speak of pre-dilution or post-dilution, depending on whether this substitute solution is added upstream or downstream from the dialyzer. The mass exchange takes place by convection in hemofiltration.
Hemodiafiltration combines the methods of hemodialysis and hemofiltration. Thus a diffusive mass exchange takes place between the patient's blood and the dialysis fluid through the semipermeable membrane of the dialyzer, and the plasma water is also filtered through a pressure gradient on the membrane of the dialyzer.
Plasmapheresis is a method blood plasma is separated from corpuscular components of blood (cells). The separated blood plasma is purified or replaced by a substitution solution and return to the patient.
In peritoneal dialysis, the patient's abdominal cavity is filled with a dialysis fluid through the abdominal wall such that the dialysis fluid has a concentration gradient with respect to the endogenous fluids. The toxic substances present in the body enter the abdominal cavity through the peritoneum, which acts as a membrane. After a few hours the dialysis fluid, now spent, which is in the patient's abdominal cavity is replaced. Water can travel from the patient's blood through the peritoneum and into the dialysis fluid by osmotic processes, thereby withdrawing water from the patient.
Dialysis methods are usually performed with the help of automatic dialysis machines such as those already distributed by the applicant under the brand name 5008 or sleep.safe.
To convey fluids in medical treatment devices, pumps of different designs are used. Peristaltic hose roller pumps are often used with machines having an extracorporeal blood circulation, such as hemodialysis machines. These hose roller pumps are often used in medical technology because they permit contactless transport of a fluid. In addition, they theoretically supply a flow which is proportional to the rotational speed over a wide range independently of the flow resistances upstream and downstream from the pump. In the case of a blood pump in extracorporeal treatment methods, the incoming (suction) side is referred to as the arterial side with an adjusted vacuum of typically approx. −100 to −300 mm mercury column in comparison with the outside pressure, and the efferent side is referred to as the venous side with a reduced pressure in comparison with the outside pressure.
DE3326785A1 discloses a typical embodiment of such an occlusive hose roller pump, according to which the delivery medium is moved by means of a periodically occluded hose.
In terms of the basic concept, a roller pump has a stator and a rotor. The stator is designed on the pump housing and has a recess with whose smoothly running vertical wall a pump hose is in contact. The area in which the pump hose is in contact with the wall forms the pump bed, which has the contour of a detail of a circle.
The axis of rotation of a rotor having rotatably mounted rollers on its free ends passes through the midpoint of this section of a circle. In rotation of the rotor in the working direction, the rollers come in contact with the pump hose, which is in contact with the circular contour of the circle of the pump bed and compress it to such an extent as it rotates further that it forms a fluid-tight seal (occlusive).
The delivery medium in the pump hose is conveyed further by further rolling of the rollers on the pump hose. In most cases, such a rotary pump has two rollers, which are mounted on the rotor in such a way that the connecting line passes through the axis of rotation of the rotor.
Other types of pumps which may be used include, for example, centrifugal pumps, diaphragm pumps or gear pumps.
The type of pump is definitive for the stress on the medium to be conveyed. This is important in particular in the case of an extracorporeal blood circulation because the blood can be damaged by pumping, and this may destroy erythrocytes, i.e., the red blood cells in particular (hemolysis). This may occur mechanically in particular, e.g., due to squeezing inside a blood hose or due to excessively high pressures.
A pulsatile non-steady-state flow, which is caused by the continuing engagement of the rollers in the pump hose segment, is characteristic of a hose roller pump. When the rollers mesh with the hose segment, the hose is squeezed together, thereby displacing the fluid. This fluid is displaced both in the direction of flow and opposite the direction of flow. Upstream from the roller, the displaced fluid is superimposed on the flow in the direction of the pump during ongoing operation and thus results in a short-term net reduction inflow, so that the arterial pressure becomes less negative until the hose is completely occluded. Then the fluid in the hose is accelerated again and the arterial pressure drops again. Downstream from the hose roller pump there is a sudden drop in pressure as soon as the roller emerges from the pump segment and a pressure equalization occurs between the reduced pressure in the segment between the rollers, this segment having been enclosed so far, and the excess pressure downstream from the pump.
Pressure peaks (and/or flow peaks) may occur in the area of the puncture site of the needle which returns the extracorporeal blood to a patient, and may cause shearing forces which in the extreme case may lead to thrombosis (coagulation) on the vascular walls and may even lead to hemolysis. Upstream from the pump, high shearing forces may also occur in equalization between high- and low-pressure systems.
In addition, hose roller pumps may also be used in the area of hemodialysis for the addition of blood-thinning substitute fluids. The pressure pulses generated in this way influence the blood to be thinned although to a lesser extent than with the blood pump at least at the location where the substitute and the blood are mixed.
Another type of pump that is used is the impeller pump or centrifugal pump. Centrifugal pumps essentially contain a housing to hold an impeller to which a magnet is fixedly connected. The magnet can be rotated by a second rotating magnet contained in a stationary base so that the impeller is made to rotate and the liquid in the housing is moved from a liquid inlet to a liquid outlet. Due to the operating principle, centrifugal pumps supply a constant volume flow so that the output pressure of the fluid pumped is a function of the input pressure, the viscosity of the fluid and the rotational speed. Pressure pulses in the fluid conveyed as in the case of peristaltic pumps do not occur with centrifugal pumps in normal operation at a constant rate of rotation of the impeller. Therefore, this prevents hemolysis caused by pulsatile conveyance of blood.
When used in the extracorporeal blood circulation, in particular in hemodialysis treatments, it is often necessary to add medication to blood in a controlled manner. A typical example of medication is the addition of anticoagulants such as heparin in hemodialysis treatments to prevent the blood from coagulating in the extracorporeal blood circulation and thereby prevent the fine hollow fibers of the dialysis filter from becoming clogged.
Syringe pumps, which add heparin or another anticoagulant (e.g., citrate) to the blood upstream from a dialysis filter, are often used for this purpose. However, it is also provided that a medication may also be added to the blood by delivering the medication through a special device and into drip chamber.
EP2386324A1 discloses such a device. A medication dosing apparatus which releases doses of a medication into the drip chamber on the basis of pressure pulses in the drip chamber is proposed there. The pressure pulses are generated here by the pulsatile non-steady-state operation of a peristaltic pump which delivers a fluid, preferably blood, into the drip chamber. Thus a pulsating air pressure characteristic develops via the fluid level inside the drip chamber in the cycle of the peristaltic pump, leading to regular dispensing of droplets of medication into the drip chamber.
So far, when using steadily delivering peristaltic pumps, it has not been possible to control the dosing of medication in a variable manner, i.e., to suspend it or have it occasionally occur more often. With centrifugal pumps it has not been possible at all so far to operate the medication dosing apparatus proposed in EP2386324A1 because of the lack of pressure fluctuations.